Also, double check this Radical Reference site itself - we have had many questions on prison statistics - though I don't recall finding sources that would answer this specific question, for those that I helped answer. In our search box at upper right, try: prisons and statistics (6 hits); prisoners and statistics gets 11 hits besides the first answer to this question.
Pubmed.gov gets 278 hits for the search: prison inmates and health and age; 47 hits even if you click on the "Limits" tab just to lower left of the search box, and click on "Links to free full text". I get 2 full text ones for: prison and health care and costs and age (out of 6 total); the same 2 full text (out of 8) for: prison and health care and cost and age; 20 free fulltext (of 89) for prison and cost and age groups; and 14 (58) for: prison and costs and age groups. As you probably have guessed by these examples, Pubmed does not allow truncation; and I might add that Google gets inconsistent results using the asterisk to truncate words.